The present invention relates to stackable block members and a method of using the block members to build retaining walls. More particularly, the present invention relates to stackable, pre-cast block members having an improved connection mechanism allowing retaining walls to be anchored in place so as to minimize movement of the block members after construction.
Retaining walls have long been used to prevent berms, slopes and embankments from sliding and slumping. Additionally, retaining walls are used as one mechanism to control soil erosion. These structures are often used to support naturally occurring slopes and embankments while also accommodating the construction of artificial slopes, embankments, planters, stairways, stream banks and similar earthworks. In these applications Pre-cast concrete blocks are a particularly useful and versatile material for constructing retaining walls.
A number of complex, and expensive, retaining wall systems have been developed for building relatively tall retaining walls (i.e. those over about 12 feet in height). The construction of such tall retaining walls typically involves (or requires) soil studies and professional engineering support. In typical conditions, retaining walls up to approximately 40 inches in height may be constructed from concrete blocks of reasonable size and the concrete blocks alone are sufficient to prevent sliding and slumping. These relatively short walls are often designed and built by contractors and home owners and do not require either soil studies or professional engineering support.
Many applications exist which require retaining walls taller than 40 inches in height, including commercial/industrial applications. Generally speaking, concrete blocks of reasonable size alone are not sufficient for these retaining walls and some method of holding the concrete blocks in position is required.
As one example of an engineered solution, a three-block system which uses wall blocks mechanically connected to and anchored by a trunk block and a tail block is shown in U.S. Pat. No. 5,350,256 to Hammer. In that system, each of the wall blocks in each course of wall blocks is connected to a trunk block which is in turn mechanically connected to a tail block. The combination of the trunk block and the tail block serves to anchor the wall block. The relative sizes of the blocks used in that system are such that the weights of the trunk block and the tail block are each nearly as great as the weight of the wall block. Unfortunately the number of trunk and tail blocks required, and the labor necessary to lay those additional blocks drives up the cost of constructing such a retaining wall.
U.S. Pat. No. 5,820,304 to Sorheim et al. describes an alternate system to achieve anchoring of the wall. More specifically, a network of uniform anchor blocks can be attached to facing blocks to provide the necessary anchoring behind the wall.
Additional systems of wall blocks which rely upon a mechanical connection between wall blocks in adjacent courses are shown in U.S. Pat. No. 5,294,216 to Sievert, and U.S. Pat. No. 5,505,034 to Dueck. Such systems rely upon the weight of the wall blocks and are not sufficient for building retaining walls of even an intermediate height.
A method of anchoring wall blocks with a lattice-like grid (i.e., “geogrid”) connected to the wall blocks is shown in U.S. Pat. No. 5,511,910 to Scales. Such grids are positioned between stacked wall blocks and extend rearwardly away from the blocks. The grids are then buried within fill material behind the retaining walls to anchor the blocks in place. While attachment of the geogrid is conveniently achieved, this structure becomes difficult to use with larger blocks (e.g. 24″×36″ blocks).
Another alternative to the design disclosed in the '910 patent to Scales is illustrated in FIG. 1. As shown in FIG. 1, each wall block includes a channel on a top surface thereof that is structured to receive an elongate bar member. A grid structure is wrapped around the elongate bar member prior to positioning the bar member within the channel. The grid structure is then routed toward the rear of the block, and a second block is stacked on top of the first block. As a result, the grid structure is “sandwiched” between the first and second blocks.
One problem with designs such as those disclosed in the '910 patent to Scales and illustrated in FIG. 1 is the interference of the grid structure with successively stacked blocks. In particular, the grid structure introduces an additional thickness between the top surface of a first block and the bottom surface of a second block stacked on top of the first block. For example, the thickness of the grid structure may be about 0.125 inches. However, as more and more blocks are stacked on top of one another, the combined thickness of each grid structure adds up quickly and causes the retaining wall to “lean forward” (i.e., become “non-vertical”) and lose stability.
Generally, most prior retaining wall block assemblies utilized friction between wall face units to generate a “connection.” Differential settlement or other problems would often diminish or eliminate this connection. Other types of connections included, for example, a bar “botkin connection.” However, this type of connection had a lesser capacity than the grid structure itself, making the connection the weak link.
Therefore, a need exists for a retaining wall system which: (a) utilizes pre-cast wall blocks of large size and weight; (b) provides a cost effective method of anchoring the wall blocks; (c) eliminates the positioning of a grid structure between the top surface of one wall block and the bottom surface of another wall block; and (d) can be built to significant heights while minimizing the risk of tipping or becoming otherwise unstable.